Lithographic printing has long been the most widely used printing technique, especially for short to medium printing run lengths of 1,000 to 15,000. The term "lithographic" is meant to include various terms used synonymously, such as offset, offset lithographic, wet lithographic, planographic, and others. Most lithographic plates are still produced photographically. The disadvantages of this and some of the alternative lithographic plate materials and processes are described in U.S. Pat. Nos. 4,958,563 and 5,487,338.
With the advent of the computer in revolutionizing the graphics design process leading to printing, there have been extensive efforts to develop a convenient and inexpensive computer-to-plate system, particularly for use in lithographic printing. Many of the new computer-to-plate systems are large, complex, and expensive. They are designed for use by large printing companies as a means to streamline the prepress process of their printing operations and to take advantage of the rapid exchange and response to the digital information of graphics designs provided by their customers. There remains a strong need for an economical and efficient computer-to-plate system for the many smaller printers who utilize lithographic printing.
A number of electronic, non-impact printing systems have been investigated for use in making lithographic printing plates to satisfy the needs of these smaller printers. Foremost among these have been laser printing systems, for example as described in U.S. Pat. No. 5,304,443 and references therein. These have had some limited success, but have not been able to overcome the disadvantages of undesired background toner imaging, limitation to small sizes (approximately 11 inches by 18 inches) which are too small for many applications, and limitation to only those flexible substrates such as paper and plastic films which can transport through the laser printers.
Another non-impact printing system which has received attention for economical and convenient computer-to-plate preparation for lithographic printing is thermal transfer printing, for example, as described in U.S. Pat. No. 4,958,564. This involves the printing of a hydrophobic wax or resin material on to the lithographic printing blank. This approach has similar size and flexible substrate limitations as described above for laser printing. In addition, the nature of the thermal transfer process is very demanding on intimate contact of the wax or resin donor ribbon to the receiver substrate to obtain consistent image quality. For this latter reason especially, the low cost thermal transfer printers in wide use for hard copy color output printing from computers are not used to prepare lithographic printing plates. Instead, more expensive, specially built thermal transfer printers have been proposed. The only widely used printers for hard copy computer output that have seen some use in making lithographic plates are laser printers, in spite of their aforementioned disadvantages.
In recent years, ink jet printers have replaced laser printers as the most popular hard copy output printers for computers. Some of the competitive advantages of ink jet printers have been low cost, reliability, and the ability to make color images without significantly increasing the cost of the printer. Both thermal ink jet and piezoelectric ink jet printing methods have been widely adopted for desktop computer printing. A third conventional type of ink jet printing, a continuous flow type method, has found acceptance in high quality color printing and proofing in graphics applications.
In spite of the very large and rapidly growing installed base of low cost desktop ink jet printers as well as a large number of higher cost, larger size ink jet printers used in prepress proofing and in printing output, there has not been use of these ink jet printers to make lithographic printing plates. There have been some reports in the literature proposing the use of ink jet printers to make lithographic printing plates. In Japanese Kokai 62-25081, an oleophilic liquid or fluid ink was printed by ink jet printing on to a hydrophilic aluminum surface of a lithographic printing plate. Titanate or silane coupling agents were present in the ink.
An ink jet printing apparatus to make lithographic printing plates is described in PCT WO 94/11191. It is directed to depositing hydrophobic or hydrophilic substances on hydrophobic printing plates.
In U.S. Pat. No. 5,501,150, a fluid ink and hydrophilic media set containing materials to produce a silver-reducible image by ink jet printing are used to make a metallic silver image which, following wet processing to make the silver image sufficiently hydrophobic, is said to provide a lithographic printing plate.
Ink jet printing where the ink is a solid or phase change type ink instead of a liquid or fluid type ink is described in U.S. Pat. No. 4,833,486 to deposit a hot wax on a surface of an offset plate. Upon cooling of the wax, it solidifies, thereby providing a printing plate. Solid ink jet printing has serious disadvantages for lithographic plates in that the wax or resin image has limited durability due to its thermoplastic, chemical, and adhesive properties and the amount and rounded shape of the solidified ink jet droplet on the media do not have the intrinsic image resolution properties found in liquid or fluid ink jet printing.
There is also prior art in the use of ink jet printing to apply an opaque image or mask pattern to a photosensitive lithographic printing plate blank, as for example, in Japanese Kokai 63-109,052. The blank is then exposed through the ink jet imaged mask pattern and then processed by conventional means to provide a lithographic printing plate. This approach retains the materials and processing of conventional lithographic printing plates and only uses ink jet printing as an alternative in the photomask through which the conventional plates are exposed. Thus this approach adds to the complexity and expense of the platemaking process and does not depend on the ink jet ink image for the hydrophobic image of the plate. U. S. Pat. No. 5,495,803 describes a solid or phase change type of ink jet printing to form a photomask for a printing plate.
Much of the technical development in ink jet printing has been directed to color and black imaging for computer hard copy output. The need for more archival, durable, and waterfast imaged media has led to ink jet inks and receiver media that containchemically reactive components. For example, U.S. Pat. No. 5,429,860 describes a reactive ink jet ink/media set where the receiver media has a reactive component which reacts with the ink to give a more durable image and reacts in the non-image areas to give a durable coating. This patent is directed solely to durable colorant imaging elements and has no teaching on durable oleophilic material imaging elements or production of lithographic printing plates, which are the subjects of the present invention. Other prior art, as for example, U.S. Pat. 5,006,862 describes the use of reactive colorants in the liquid ink jet ink or fluid to provide more durable, waterfast, and bleed resistant images when printed on the media. These approaches for archival, more durable color and black ink jet images do not address the requirements for a durable hydrophobic image suitable for a lithographic printing plate. It would be advantageous to have a liquid ink jet ink or fluid that could be used on the large installed and future base of ink jet printers, now used extensively to print colorants on media, to print a durable oleophilic and water-insoluble image, particularly for use on a suitable lithographic printing plate blank to make a lithographic printing plate.
Accordingly, it is an object of this invention to provide a liquid ink jet ink or fluid that provides an oleophilic, durable, and water-fast image upon ink jet printing.
Another object of this invention is to provide a liquid ink jet fluid-media set that provides an oleophilic, durable, and water-fast image with a hydrophilic, durable non-image area. It is a further object of this invention that this liquid ink jet fluid-media set provides an imaged printing plate suitable for high quality lithographic printing.
It is a further object of this invention that the liquid ink jet fluid-media set be capable of being printed on conventional, low cost desktop ink jet printers to provide an imaged printing plate suitable for high quality lithographic printing. Yet another object of this invention is that the liquid ink jet fluid-media set is capable of being printed on conventional large format ink jet printers with printing widths and lengths in excess of 24 inches to provide an imaged printing plate suitable for high quality lithographic printing. Still another object of this invention is that the liquid ink jet fluid-media set is capable of being printed on ink jet printers of all sizes with a wider choice of rigid and flexible media than with laser and other non-impact printers to provide an imaged printing plate suitable for high quality lithographic printing.
It is a further object of this invention that no wet processing step, before or after the ink jet printing, is required to provide an imaged printing plate suitable for high quality lithographic printing.
It is another object of this invention that no colorant is required in the liquid ink jet fluid to provide an oleophilic, durable, and waterfast image and to provide an imaged printing plate suitable for high quality lithographic printing.
It is a further object of this invention that no metal precursor is required in the liquid ink jet fluid or the media and no metal is required in the image areas to provide an oleophilic, durable, and water-fast image and to provide an imaged printing plate suitable for high quality lithographic printing.
Still another object of this invention is to provide a convenient and economical method to provide an imaged printing plate suitable for high quality lithographic printing.
These and other objects of the present invention will become apparent upon a review of the following specification and the claims appended thereto.